Shapechanger. The yuan-ti can use its action to polymorph into a Medium snake, or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It doesn't change form if it dies.

Innate Spellcasting (Yuan-Ti Form Only). The yuan-ti's innate spellcasting ability is Charisma (spell save DC 14). The yuan-ti can innately cast the following spells, without providing material components:

At will: animal friendship(snakes only)

3/day: suggestion

Magic Resistance. The yuan-ti has advantage on saving throws against spells and other magical effects.

Spellcasting. The yuan-ti is a 5th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 14, +6 to hit with spell attacks). It has the following cleric spells prepared:

Cantrips (at will): guidance, sacred flame, thaumaturgy, toll the dead

1st level (4 slots): bane, command, divine favor, guiding bolt, healing word, shield of faith

2nd level (3 slots): hold person, magic weapon, silence, spiritual weapon

3rd level (2 slots): bestow curse, crusader's mantle, spirit guardians

Multiattack (Yuan-Ti Form Only). The yuan-ti makes two ranged attacks or two melee attacks, but can constrict only once.

Bite (Snake Form Only). Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 5 (1d4 + 3) piercing damage plus 7 (2d6) poison damage.

Constrict. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the yuan-ti can't constrict another target.

Morningstar (Yuan-ti Form Only). Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage.

Longbow (Yuan-ti Form Only). Ranged Weapon Attack: +5 to hit, range 150/600 ft., one target. Hit: 6 (1d8 + 2) piercing damage plus 7 (2d6) poison damage.

Guided Strike (Recharges after a Short or Long Rest). The yuan-ti grants a + 10 bonus to an attack roll made by itself or another creature within 30 feet of it. The yuan-ti can make this choice after the roll is made but before it hits or misses.